A fatigue load of a wind turbine set in a wind farm often increases and exceeds a design load depending on an arrangement of the wind turbine and a wind condition, due to a mutual interference between wind turbines. If the wind turbine is operated without taking any measures, a failure in the wind turbine or an incident can possibly occur before a designed lifetime (20 years for a typical wind turbine, for example). Therefore, measures of limiting operating hours by shutting down the wind turbine at a wind speed equal to or slower than a normal cut-out wind speed (25 m/s for a typical wind turbine) in a wind direction in which an influence of the wind turbine interference is large, thereby reducing the fatigue load are commonly taken. This is called a curtailment strategy. When the curtailment strategy is carried out, the operating hours become shorter, and naturally, energy production reduces as well.
Therefore, in order to minimize the loss in energy production, there has been proposed a method of carrying out a preliminary assessment, and determining a condition setting value for the curtailment for the wind turbine to be as appropriate as possible (see Non-Patent Citation 1, for example). By carrying out the preliminary assessment in this manner, it is expected to avoid too much curtailment and ensure desired energy production.